Why does Data Expire on Pay as you Go

Firstly i tried to log this on your Website but it just gives me a red \X\" with noting to go on as to what the problem might be.<br> <br> Can you please advise why on pre-paid my Data expires?<br> <br> i purchased the 1Gig data with my own money so it should stay on my phone until it is depleted should it not? you may have given me another gig free but i have not even used my own 1 gig as yet.<br> <br> There is not a single place on you site that i can find that advises clients that data will expire in exactly 1 calendar month. <br> <br> It would be nice to know why you are *****ing my data like this.<br> <br> If your response to me is not satisfactory i will need to log a complaint with the NCR for goods or services not delivered."